The invention concerns equipment in the system of rolls in a supercalender for equalizing the profiles of linear loads between the rolls, said system of rolls comprising an upper roll, a lower roll, several intermediate rolls placed between the upper roll and the lower roll, as well as lifting spindles placed at both sides of the system of rolls.
The system of rolls in a conventional supercalender comprises a number of rolls, usually 8 to 14 rolls, which are arranged one above the other as a stack of rolls. The rolls placed one above the other are in nip contact with each other, and the paper web to be calendered is arranged to run through the nips between the rolls. The rolls in the system of rolls are mounted rotatably in bearing housings, which are provided with fastening brackets that are fitted as freely gliding on vertical lifting spindles. Thus, one of the functions of the lifting spindles is to act as guides so as to keep the rolls in the system of rolls in the correct position. Thus, the bearing housings of the rolls in the system of rolls are not fixed rigidly to the calender frame, but the bearing housings, and consequently also the rolls, can move vertically. Since the masses of the bearing housings of the rolls and of the auxiliary devices attached to same are quite large, in conventional supercalenders this causes the considerable drawback that said masses of the bearing housings and of the auxiliary devices attached to same cause distortions in the distributions of the linear loads in the nips between the rolls. Thus, the linear load in the nips is not uniform, but it is substantially higher at the ends of the nips than at the middle. Since in the systems of rolls of supercalenders there are several rolls placed one above the other, as was already stated above, this further results therein that the faults in the linear loads in individual nips are cumulated and cause a considerably large error in the overall linear load. This defective distribution of the linear load deteriorates the quality of the calendered paper.
So far, attempts have not been made to find a solution for the problem described above, and this is why the object of the present invention is to provide an equipment by means of which it is possible to eliminate the errors in the profiles of the linear loads in the nips which are caused by the masses of the bearing housings of the rolls in the system of rolls and by the masses of the auxiliary devices attached to the bearing housings. From conventional machine calenders, a solution is known in prior art wherein the rolls of the machine calender are provided with a lightening system, in particular with hydraulic lightening cylinders for elimination of concentrated loads arising from the bearing housings of the rolls and from auxiliary devices. It is a simple matter to provide machine calenders with such relief devices, because the rolls in the system of rolls of a machine calender are mounted on the frame of the calender by the intermediate of levers with articulated joints. It would be very difficult and even impossible to use devices corresponding to the machine calenders in supercalenders because of the constantly varying diameters of the fibre rolls and of the large number of rolls in supercalenders.